1. Field of the Invention
The present invention relates to a positioning apparatus for positioning a plate-shaped article such as a semiconductor wafer without contact with the article and an exposing apparatus having this positioning apparatus.
2. Related Background Art
For a photolithography process for manufacturing a semiconductor device, a liquid crystal display device, a thin-film magnetic head or the like, a projecting/exposing apparatus (a stepper or the like) for transferring a pattern of a reticle used as a mask onto each shot region on a wafer (or a glass plate or the like) used as a photosensitive substrate through a projection optical system and an exposing apparatus or the like using a proximity method for transferring the reticle pattern directly on the wafer have been heretofore used. Since such an exposing apparatus is required to position the wafer in an exposure position with high precision, the wafer is held on a wafer holder by a vacuum absorption or the like and this wafer holder is fixed on a wafer stage capable of being positioned with high precision or the wafer stage capable of roughly slightly moving.
FIG. 17 shows an example of the wafer stage of the prior-art exposing apparatus. Referring to FIG. 12, a Y stage 102 is placed on a wafer base 101 so that it may be driven in a Y-direction by a driving motor, and an X stage 103 is placed on the Y stage 102 so that it may be driven in an X-direction by the driving motor. Furthermore, a mounting support 104 is mounted on the X stage 103, a wafer holder 105 is fixed on the mounting support 104, and a wafer 106 is held on the wafer holder 105 by the vacuum absorption. Movable mirrors 107, 108 for a laser interferometer are also fixed near the wafer holder 105 on the mounting support 104 so that they may be perpendicular to each other. In this case, the mounting support 104 can position the wafer 106 in a Z-direction and in a direction of rotation about an axis parallel to a Z-axis and can correct an inclined angle of the wafer 106 (that is, an angle of rotation about the axes parallel to an X-axis and a Y-axis).
When a deformation such as a local curvature is caused on the wafer, a reticle image is not transferred on the shot region near such a deformed region with high resolution. Therefore, proposed is the method in which many piezoelectric devices are buried in parallel in the wafer holder 105 and an amount of expansion/contraction (deformation) of these piezoelectric devices is partially controlled so as to thereby improve a flatness of the wafer held on the wafer holder 105.
FIG. 18 shows an example of the prior-art wafer holder. In FIG. 18, many absorbing grooves 102 are formed on a contact surface of a front surface of a wafer holder 101a with a wafer W. Air or the like in the absorbing grooves 102a is evacuated through an exhaust path 103a in the wafer holder 101, whereby the wafer W is absorbed/held on the front surface of the wafer holder 101a. On the other hand, when the thus absorbed/held wafer W is locally deformed (curved), the reticle image cannot be excellently exposed depending on the shot region on the wafer W.
As shown in FIG. 19, the wafer holder capable of correcting the flatness of the wafer is also proposed. In FIG. 19, a space is provided in a bottom portion of the exhaust path 103a in the wafer holder 101a, and many expandable/contractible piezoelectric devices 104 are attached in this space. Therefore, the amount of expansion/contraction (deformation) of the piezoelectric devices 104a is individually controlled so that the region on the front- surface of the wafer holder 101a on the piezoelectric devices 104 is deformed, whereby the flatness of the wafer W absorbed/held on the region can be improved.
FIG. 20 shows an example of the conventional wafer stage. In FIG. 20, a Y stage 106 is placed on a wafer base 105a so that it may be movable in the Y-direction, and an X stage 107 is placed on the Y stage 106a so that it may be movable in the X-direction. A slight moving stage 109 is also mounted in the X stage 107a by using four elastic hinges 108A-108D as a guide so that it can be slightly moved in the X-direction by piezoelectric devices 111, 112. The wafer W is fixed on a mounting support 113 through the wafer holder 101a. Movable mirrors 116X, 116Y for the laser interferometer are also fixed near the wafer holder 101. In this case, the X stage 107 and the Y stage 106 are operated as a rough moving stage so as to roughly position the wafer W. Then, the slight moving stage 109 and the mounting support 113 are slightly moved in the X-direction and the Y-direction, respectively, whereby the wafer W is positioned with high precision.
As described above, the wafer stage of the prior-art exposing apparatus is composed of various stages and the mounting support stacked on the wafer base. Positioning of the wafer on the mounting support is performed by, for example, the driving motor using a feed screw method or the like. As regards this fact, it has been recently needed to further improve the positioning precision of the wafer stage in response to a finer formation of the semiconductor device or the like. Moreover, since an improvement of throughput (productivity) is desired in the process of manufacturing the semiconductor device or the like, the improvement of a positioning speed of the wafer stage is also required.
Although the driving motor having a high power is needed in order to position the mounting support (wafer) at high speed with high precision by means of this conventional stacked-structure wafer stage, the use of such a driving motor causes an apparatus constitution to be large-sized and be heavy in weight. As a result, the positioning speed cannot be disadvantageously improved so much. Furthermore, if the high-power driving motor is used, the mounting support and the wafer are deformed due to heat by an influence of the heat generated by the driving motor, and thus there is a possibility that the positioning precision is deteriorated rather than improved.
In the prior art in which many piezoelectric devices are buried in the wafer holder in order to improve the local deformation of the wafer, it is also necessary to dispose many high-voltage wires for use in the piezoelectric devices in the wafer holder. Thus, the wafer holder is large-sized and the positioning speed is thus reduced, and a manufacturing cost is also disadvantageously increased.
In the above-described prior art, in case of the wafer holder of FIG. 18, the wafer W is held on the wafer holder 101 by the vacuum absorption. Thus, if a contaminant such as resist residue is put between the rear surface of the wafer W and the front surface of the wafer holder 101, the wafer W is deformed due to the contaminant. As a result, there is a possibility that a yield of a semiconductor device to be finally manufactured is reduced. On the other hand, in case of the wafer holder of FIG. 20, the flatness of the wafer W is corrected by the expansion/contraction of many piezoelectric devices 104 in the wafer holder 101. However, disadvantageously, since this method is required to arrange many high-voltage wires for the piezoelectric devices, the apparatus constitution is increased in size and complicated, which results in the higher cost.
Moreover, in the conventional wafer stage of FIG. 20, when the position of the image projected on the reticle matches to that of each shot region on the wafer, the wafer W is stepped at high speed through the X stage 107 and the Y stage 106 (the rough moving stage). Then, the slight moving stage 109 and the mounting support 113 are slightly moved through the piezoelectric devices 111, 112 and 114, 115, whereby the wafer W is finally positioned. However, for a structure for adjusting the position by pushing/pulling the slight moving stage 109 and the mounting support 113 by the piezoelectric devices, the high-speed positioning is difficult. Furthermore, since the slight moving stage 109 is large-sized and heavy in weight, the rough moving stage for driving the slight moving stage 109 at high speed requires a high thrust force. Thus, the whole stage is large-sized and a heat value gets higher, which may cause a deterioration of the positioning precision.